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Math Help - Geometric progression

  1. #1
    Newbie parmis's Avatar
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    Geometric progression

    Geometric progression-gggg.jpg
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  2. #2
    Forum Admin topsquark's Avatar
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    Re: Geometric progression

    Quote Originally Posted by parmis View Post
    Click image for larger version. 

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    I'm going to take a guess here. Is this your problem?

    a_n = \frac{(m^2 - a)n^2 +m + n}{m^2 + 2m + 1}

    But that can't be right...the a on the RHS needs a subscript, doesn't it?

    -Dan
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  3. #3
    Newbie parmis's Avatar
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    Re: Geometric progression

    Oh... sorry i made a mistake. a n is Arithmetic progression! d=1/5
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  4. #4
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    Re: Geometric progression

    So a_n is an arithmetic progression of the form a_n= a+ nr but what does "m" represent in your formula?
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  5. #5
    Newbie parmis's Avatar
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    Re: Geometric progression

    I dont know. My teacher gave me this, but i cant answer it!
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  6. #6
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    Re: Geometric progression

    Then you should probably ask your teacher what m means.
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  7. #7
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    Re: Geometric progression

    Quote Originally Posted by parmis View Post
    Oh... sorry i made a mistake. a n is Arithmetic progression! d=1/5
    Assuming your arithmetic progression is a_n = a+dn since you arbitrarily wrote a d for some reason, we can set these two expressions equal to each other:

    a_n = a+dn

     = a+\dfrac{n}{5} = \dfrac{(m^2-a)n^2+m+n}{m^2+2m+1}

    If you are trying to solve for m, it is the solution to this quadratic equation in m:

    \left(a+\dfrac{n}{5}-n^2\right)m^2 + \left(2a + \dfrac{2n}{5}-1\right)m + \left(a+an^2-\dfrac{4n}{5}\right) = 0

    You can use the quadratic formula. You get a mess, but I suppose that could be the solution for m...
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